Smooth bore collar

ABSTRACT

A friction-reducing device for use in a well bore, the friction-reducing device being cylindrically shaped with a tapered and partially threaded upper section, cylindrical middle section, and tapered and partially threaded lower section. The middle section comprises a cylindrical outer surface, cylindrical inner surface, solid portion between the cylindrical outer surface and the cylindrical inner surface, and first plurality of friction-reducing units. The friction-reducing units are installed at equally-spaced angular intervals into ports within the solid portion of the middle section in a circular array that lies in a first plane that is perpendicular to a longitudinal axis of the cylindrical bore in the friction-reducing device. Each friction-reducing unit comprises a rear bearing seat, an array of miniature ball hearings, and a main ball bearing with a protruding portion that extends through the inner surface of the middle section into the cylindrical bore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of oil well devices that reduce friction between a string of production tubing and a string of sucker rod positioned within the production tubing. More particularly, the present invention relates to those devices that are threadably installed in-line within a string of production tubing and that comprise ball bearings as a friction-reducing mechanism.

2. Description of the Related Art

Although there are a number of issued U.S. patents and patent applications that describe friction-reducing devices for use with oil well drill strings and production, strings, none of these prior art inventions includes the novel features of the present invention. Those features include threaded in-line couplings and friction-reducing ball bearings that make direct contact with a sucker rod positioned within the bore of the invention and that are freely rotatable around any axis of rotation.

U.S. Pat. No. 1,888,216(Bull, 1932) discloses a device for reducing rotational friction between a drill pipe and the sides of a borehole. The invention comprises a cylindrical collar that fits around a section of drill pipe, and the collar comprises a plurality of ball bearing assemblies that allow the drill pipe to rotate within the collar. The invention incorporates gripping plugs with teeth to secure the collar at a fixed position around the outside surface of the drill pipe.

U.S. Pat. Nos. 1,890,529 and 1,890,530 (Santiago, 1952 ) disclose a drill stem bearing device that fits around drill pipe, pump rods, or similar well equipment (referred to generally as “stems”). The invention is attached to a stem via a pair of clamping rings that secure the device against longitudinal movement with respect to the stem. The device provides a rotatable collar comprising an annular ring of sleeves or rollers to reduce rotational friction between the collar and the stem to which it is attached. The sleeves are in the form of non-rotatable ribs, and the rollers are shown as being cylindrical in shape, with each roller comprising an axial pin and each axial pin oriented parallel to the axis of the stem. The sleeves or rollers are enclosed within a segmented carrier.

U.S. Pat. No. 1,911,365 (Bailey, 1933 ) discloses an anti-friction bearing that fits around a drill stem to reduce friction between the drill stem and the surrounding well casing. The invention is generally in the shape of a hollow cylinder or collar. The invention comprises a plurality of annular rollers, with at least one set of rollers oriented so as to reduce axial (longitudinal) friction and at least one other set of rollers oriented so as to reduce rotational friction. The rollers are shown in the drawings as being cylindrical in shape, but are described [page 2, lines 54-55] as being “any suitable shape, either cylindrical or spherical”. Each roller rotates around a rigidly positioned axial pin so that the axis of rotation is fixed for each roller.

The rollers that are oriented so as to reduce rotational friction (the “rotational rollers”) are positioned so that a portion of each rotational roller extends into the hollow interior of the device, thereby causing each of these rotational rollers to contact the drill stem. The rollers that are oriented so as to reduce axial friction (the “axial rollers”) are positioned so that a portion of each of these axial rollers extends beyond the outside perimeter of the collar of the device, thereby allowing some of the axial rollers to contact well casing when the drill stem comes into close proximity with one side of the well casing. This arrangement of the two sets of rollers allows the drill stem to rotate within the device using the rotational rollers as bearings and also allows the drill stem to move up and down within the well casing using the axial rollers as bearings.

U.S. Pat. No. 2,127,796 (Willis, 1938) discloses two embodiments of a bearing structure for use in oil wells. Both embodiments of the invention are designed to allow free passage of oil and gas through the invention while reducing friction between certain moving parts within the well. The first embodiment of the invention is designed to centralize a well tubing within a well casing and reduce friction between the tubing and casing. The first embodiment is designed to be installed around the outside of a tubing string. This embodiment comprises a plurality of hail bearings that are positioned between a sleeve and a collar of the invention. Installation of the first embodiment around a section of well tubing requires molten metal to be poured around the well tubing to form a liner for the first embodiment.

The second embodiment of the invention is designed to centralize a specially-shaped sucker rod within a curved tubing string and reduce friction between the sucker rod and tubing string. The second embodiment is slidably attached around the sucker rod and is held in place against the inner surface of the tubing string by friction. See p. 2 , lines 32-33 (“collar is secured in frictional engagement to the inner periphery of the tube 6 due to inflection of the tube and thereby serves to maintain the sucker rod in spaced relation from said tube”). The second embodiment comprises a plurality of ball bearings that are positioned between a collar in the body of the device and longitudinal grooves that are manufactured into the outer surface of the specially shaped sucker rod. Unlike the present invention, the second embodiment of the Willis invention is not designed to be used in combination with standard (non-grooved) sucker rod, nor is the ball bearing mechanism constructed so as to allow the sucker rod to rotate within the tubing string.

U.S. Pat. No. 2,499,252 (Michael, 1950) discloses an earth-boring tool designed to be lowered into well casing and to drill into soil or rock below the open-ended bottom of the casing. The invention comprises a rotatable drive shall that is attached to a rotatable cutting head. The drive shaft is centered within the casing by a bearing member that is installed around the drive shaft and that fits between the inside surface of the casing and the outside surface of the drive shaft. The bearing member comprises a friction-reducing ball bearing assembly or conventional design—i.e., the bearing assembly is generally ring-shaped and comprises ball bearings or rollers positioned between a circular outer race and a circular inner race.

U.S. Pat. No. 2,758,891 (Klammerer, 1956) discloses a stabilizing device used to center a drill string within a well bore and reduce axial friction of the drill pipe that comes into contact with the walls of the well bore. The device is installed around a drill collar that is located between the bottom piece of drill pipe and the drill bit. The device comprises an inner sleeve and an outer collar. When the drill pipe is rotated, the inner sleeve rotates with the drill pipe, but the outer collar does not rotate. The device comprises two conventional ball bearing assemblies that are positioned between the sleeve and collar.

U.S. Pat. No. 6,585,043 (Murray, 2003) discloses a friction-reducing centralizer used to reduce axial and rotational drag between an oil well tubular and the wall of a well. The invention is designed to fit around the tubular and may be secured in position with stock collars optionally provided at each end of the invention. This invention comprises a plurality of rollers, with a first group of rollers designed to reduce friction between the centralizer and the tubular and a second group of rollers designed to reduce friction between the centralizer and the wall of the well. All of the rollers rotate around axles that are fixed within the body of the centralizer. The first group of rollers has an axis of rotation generally parallel to the axis of the tubular, and the second group of rollers has an axis of rotation that is generally transverse to the axis of the tubular. The first group of rollers is positioned so that a portion of each of the rollers projects through an opening in the inside surface of the invention, so as to contact the outside surface of the tubular member within the centralizer. The second group of rollers is positioned so that a portion of each roller projects through an opening in the outside surface of the invention, so as to contact the wall of the well when the tubular comes into close proximity to the wall of the well. All of the rollers are preferably cylindrical in shape with tapered ends.

U.S. Patent Application Pub. No. 2002/0020526 (Male et al.) discloses a well casing centralizer device that is designed reduce friction between the outside surface of the casing and the wall of the well when the casing is being installed into the well bore. The invention is described [paragraph 0009, lines 4-5] as being attachable to the casing: “may be disposed about a casing joint or indeed connected into the casing string through a threaded coupling . . . . ”The descriptions of the invention, however, only describe an embodiment that is slipped over the casing. See paragraph 0025, describing FIG. 1: “In order to assemble the centralizer on the casing joint CJ, the body of the centralizer is slipped over the pin end of the joint prior to make up of the pin with a box end on an adjacent casing joint.”

The invention is generally tubular in shape with longitudinal fins manufactured into the outer surface. Each of the fins contains a plurality of individual friction-reducing elements, and each of the friction-reducing elements comprises a rotatable ball bearing. The plurality of friction-reducing units is positioned along the outer surface of each fin. In the embodiment described in reference to FIG. 2a, each friction-reducing unit comprises a threaded front bearing seat, an unthreaded rear bearing seat, and a plurality of “micro balls” between the rear bearing seat and the rotatable ball bearing. A portion of each ball bearing protrudes beyond the outer surface of the fin so that the ball bearing contacts the wall of the well when the fin comes into close proximity to a wall of the well thereby reducing frictional drag between the fin and the wall of the well when the casing is rotated or moved longitudinally.

Unlike the present invention, this invention does not provide a low-friction bearing surface between the bore of the device and a tubular member installed within the bore of the device but instead reduces friction between the outside surface of the device and well casing that surrounds the device. The friction-reducing units (i.e., the ball bearing mechanisms) of the Male invention are dissimilar to those of the present invention in that each of the Male units comprises a front bearing seal that is threadably attachable into blind bores incorporated within the body of the device. By contrast, in the present invention, the front bearing seal of each friction-reducing unit is manufactured into the body of the device rather than being a separate part.

In summary, none of the prior art examples cited above incorporates the novel features of the present invention, which most notably include a plurality of ball bearings that partially protrude into the bore of the invention, wherein each ball bearing is capable of free rotation around any three-dimensional axis, and wherein the invention is installable in-line between two lengths of production tubing with threaded connections.

BRIEF SUMMARY OF THE INVENTION

The present invention is a friction-reducing device for use in a well bore, the friction-reducing device being cylindrically shaped with a tapered and partially threaded upper section, a cylindrical middle section, and a tapered and partially threaded lower section; wherein the middle section comprises a cylindrical outer surface, a cylindrical inner surface, a solid portion between the cylindrical outer surface and the cylindrical inner surface, and a first plurality of friction-reducing units; wherein the inner surface of the middle section forms a cylindrical bore in the center of the friction-reducing device, the cylindrical bore having a constant diameter from top to bottom; wherein the friction-reducing units are installed at equally-spaced angular intervals into ports within the solid portion of the middle section in a circular array that lies in a first plane that is perpendicular to a longitudinal axis of the cylindrical bore; wherein each friction-reducing unit comprises a rear bearing seat, an array of miniature ball bearings, and a main ball bearing with a protruding portion that extends through the inner surface of the middle section into the cylindrical bore of the friction-reducing device; wherein each port extends through the solid portion and penetrates both the outer surface and the inner surface of the middle section; wherein each port comprises a three-dimensional concave portion that penetrates the inner surface of the middle section; wherein the rear bearing seat of each tried friction-reducing unit comprises male threads around an outside circumference of the rear bearing seat that mate with female threads on an inside surface of the port; wherein the rear bearing seat further comprises a hex socket on an outside end of the rear bearing seat and a three-dimensional concave indentation on an inside end of the rear bearing seat; wherein the main ball bearing is positioned against the three-dimensional concave portion of the port, the three-dimensional concave portion of the port forming a front bearing seat for the main ball bearing; wherein the plurality of miniature ball bearings is situated between the three-dimensional concave indentation of the rear bearing seat and a portion of the main ball bearing that faces toward the outer surface of the middle section, and wherein the plurality of miniature ball bearings provides a low-friction rolling surface between the rear bearing seat and the main ball bearing; wherein the main ball bearing is free to rotate in any direction about any three-dimensional axis; and wherein the friction-reducing device is threadably inserted in-line between two adjacent lengths of production tubing, wherein a sucker rod is inserted through the cylindrical bore of the friction-reducing device, and wherein the friction-reducing device maintains a gap between an inside wall of the production tubing and the sucker rod.

In a preferred embodiment, the upper section, the middle section, and the lower section are manufactured as a single unit from a single piece of machined steel. In an alternate embodiment, the invention further comprises a second array of friction-reducing units identical to the first array of friction-reducing units except that the second array of friction-reducing units is installed in a circular array that lies in a second plane that is perpendicular to the longitudinal axis of the cylindrical bore, wherein the first and second arrays of friction-reducing units each has an angular orientation, and wherein the angular orientation of the second array of friction-reducing units is shifted by a certain angle in relation to the angular orientation of the first array of friction-reducing units.

In a preferred embodiment, the middle section further comprises a plurality of threaded holes that extend from the outer surface into the solid portion of the middle section but do not extend to the inner surface of the middle section, and wherein the threaded holes are configured to receive attachment screws for a stabilizer; the friction-reducing device further comprising a stabilizer that is secured to the middle section of the friction-reducing device via the attachment screws, wherein the production tubing has an outside diameter and a magnitude of pulsation movement within a well casing, the stabilizer being configured to increase the outside diameter of the production tubing, thereby reducing the magnitude of pulsation movement of the production tubing inside the well casing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first side view of the first embodiment of the present invention.

FIG. 2 is a transverse cross-section view of the first embodiment taken through the center of the rear bearing seats.

FIG. 3 is a second side view of the first embodiment of the present invention.

FIG. 4 is an axial cross-section view of the first embodiment taken through the centerline of two of the rear bearing seats 5 that are located on opposite sides of the first embodiment.

FIG. 5 is a magnified detail cross-section view of a friction-reducing unit,

FIG. 6 is an exploded cross-section view of a friction-reducing unit.

FIG. 7 is a cut-away partial side view that illustrates a typical installation of the first embodiment installed within a production oil well.

FIG. 8 is a detail transverse cross-section view of the first embodiment shown with a sucker rod installed within the bore of the invention.

FIG. 9 is a side view of the second embodiment of the present invention.

FIG. 10 is a transverse cross-section view of the first array of friction-reducing units of the second embodiment.

FIG. 11 is a transverse cross-section view of the array of threaded holes of the second embodiment.

FIG. 12 is a transverse cross-section view of the second array of friction-reducing units of the second embodiment.

FIG. 13 is a side view of the third embodiment of the present invention.

FIG. 14 is a transverse cross-section view of the first array of friction-reducing units of the third embodiment.

FIG. 15 is a transverse cross-section view of the second array of friction-reducing units of the third embodiment.

FIG. 16 is a side view of a stabilizer that is designed to fit around and attach to a unit of the second embodiment or a unit of the third embodiment.

FIG. 17 is an axial cross-section view of the stabilizer.

FIG. 18 is a transverse cross-section view of the stabilizer.

FIG. 19 is a side view of the second embodiment or the third embodiment with a stabilizer installed.

REFERENCE NUMBERS

1 First embodiment of the present invention

2 Upper section

3 Middle section, first embodiment

4 Lower section

5 Rear bearing seat

6 Outer surface of middle section

7 Solid portion of middle section

8 Inner surface of middle section

9 Friction-reducing unit

10 Port

11 Bore

12 Main ball bearing

13 Protruding portion, of a main ball bearing

14 Void space within a port

15 Cup-shaped portion of port

16 Female threads of port

17 Miniature ball bearing

18 Male threads of tear bearing seat

19 Hex socket of rear bearing seat

20 Cup-shaped indentation of rear bearing seat

21 Well casing

22 Subsurface formation

23 First piece of production tubing

24 Second piece of production tubing

25 Sucker rod

26 Second embodiment of the present invention

27 Middle section of the second embodiment

28 First array of friction-reducing units of the second embodiment

29 Array of threaded holes

30 Threaded hole

31 Second array of friction-reducing units of the second embodiment

32 Third embodiment of the present invention

33 Middle section of the third embodiment

34 First array of friction-reducing units of the third embodiment

35 Second array of friction-reducing units of the third embodiment

36 Stabilizer

37 Cap screw

38 Screw hole in centralizes

39 First cap screw

40 First screw hole

41 Second cap screw

42 Bore of stabilizer

DETAILED DESCRIPTION OF INVENTION

The present invention is a friction-reducing device designed to reduce friction between oil well production tubing and a sucker rod that is installed into and moving within the bore of the production tubing and is particularly suited for use in wells having significant curvature. The present invention is threadably inserted in-line between two adjacent lengths of production tubing and serves as a low-friction centralizer to maintain a gap between the inside wall of the production tubing and the sucker rod. The present invention comprises a plurality of individual ball bearings that protrude into the bore of the invention and provide low-friction bearing surfaces between the invention and the sucker rod. For typical applications, multiple units of the invention are installed at various locations along the length of the production tubing. The present invention comprises three similar embodiments, which differ primarily in overall length and the total number of ball bearing elements utilized per unit.

FIG. 1 is a first side view of the first embodiment of the present invention. As shown, the first embodiment 1 is generally cylindrically shaped, with a tapered and partially threaded upper section 2, a generally cylindrical middle section 3, and a tapered and partially threaded lower section 4. The threads of the upper section 2 and the lower section 4 are male threads of the same size with the thread dimensions selected so as comply with standard American Petroleum Institute (API) production tubing thread specifications. The first embodiment 1 comprises six identical rear bearing seats 5, two of which are shown. The first embodiment 1 has an overall length of about 6.0 inches, a middle section 3 length of about 1.5 inch, and a maximum outside diameter of about 3.5 inches. The upper section 2, the middle section 3, and the lower section 4 are preferably manufactured as a single unit from a single piece of machined steel, which is powder-coated. The rear bearing seats 5 are preferably manufactured from hardened steel.

FIG. 2 is a transverse cross-section view of the middle section 3 taken through the center of the rear bearing seats 5, at the section line shown in FIG. . 1 . The middle section 3 comprises a cylindrical outer surface a solid portion 7, a cylindrical inner surface and six identical friction-reducing units 9. The friction-reducing units 9, which are described in detail with reference to FIGS. 5 and 6, are installed at equally-spaced angular intervals into ports 10 within the solid portion 7 of the middle section 3, in a circular array which lies in a plane that is perpendicular to the axis of the bore 11, and in winch the plane is generally through the center (as measured from top to bottom) of the middle section 3.

FIG. 3 is a second side view of the first embodiment 1, showing the upper section 2, the middle section 3, the lower section 4, three of the six rear bearing seats 5 and the outer surface 6 of the middle section 3.

FIG. 4 is an axial cross-section view of the first embodiment 1 taken through the centerline of two of the rear bearing seats 5 that are located on opposite sides of the first embodiment 1, at the section line shown on FIG. 3. As shown, the first embodiment 1 comprises a cylindrical bore 11 that has a constant diameter from top to bottom. Two of the friction-reducing units 9 are shown in vertical cross section, with the rear bearing seat 5 and a main ball bearing 12 within each friction-reducing unit 9 shown. The protruding portions 13 of two ball main ball bearings from two of the other six friction-reducing units 9 are shown extending through the inner surface 8 of the middle section 3 into the bore 11.

FIG. 5 is a magnified detail cross-section view of the friction-reducing unit 9 shown in FIG. 2, shown with the friction-reducing unit 9 threadably installed, into a port 10. FIG. 6 is an exploded view of the same friction-reducing unit 9 shown in FIG. 5, except that it has been removed from the port 10 for clarity. Note that the structure of the friction-reducing unit 9 is the same in all three embodiments discussed herein.

As shown, in FIGS. 5 and 6, the port 10 extends through the solid portion 7 and penetrates both the outer surface 6 and the inner surface 8 of the middle section 3. The port 10 is generally cylindrical in shape, with the internal void space 14 packed with lubricating and corrosion-preventative grease (not shown) and having a cup-shaped (i.e., three-dimensional concave, that is, concave from the perspective of the inside of the port and tapered in diameter from the most inward thread 16 in the port to the point at which the portion 15 meets the inner surface 8 of the middle section 3) portion 15 at the end that penetrates the inner surface 8. The port 10 comprises female threads 16 manufactured into the perimeter of the non-tapered section. The friction-reducing unit 9 is comprised of a rear bearing seat 5, a main ball bearing 12, and an array of miniature ball bearings 17. The rear bearing seat 5 comprises male threads 18 around the outside circumference that mate with the female threads 16 of the port 10, a hex socket 19 on the outside end (i.e., the end facing the outer surface 6), and a cup-shaped (i.e., three-dimensional concave) indentation 20 on the inside end (i.e., the end facing the inner surface 8).

The main ball bearing 12 is positioned against the cup-shaped portion 15 of the port 10. The dimensions of the cup-shaped portion 15 are selected so as to provide a close but non-binding fit with the spherical surface of main ball bearing 12, so that the cup-shaped portion 15 forms a front bearing seat for the main ball bearing 12. The plurality of miniature ball bearings 17 are disposed in a three-dimensional, cup-shaped array between the cup-shaped indentation 20 of the rear bearing seat 5 and that portion of the main ball bearing 12 that generally faces toward the outer surface 6.

The dimensions of the cup-shaped indentation 20 are selected so that the cup-shaped array of miniature ball bearings 17 forms a close fit around that portion of the spherical source of the main ball bearing 12 that contacts the array of miniature ball bearings 17. This configuration of the rear bearing seat 5, the miniature ball bearings 17, and the main ball bearing 12 provides a low-friction rolling surface between the rear bearing seat 5 and the main ball bearing 12. Note that the main ball bearing 12 is free to rotate in any direction about any three-dimensional axis. Also note that the shape of the inner surface 8 through which a portion of the main ball bearing 12 penetrates is convex in transverse cross section, as viewed looking from the outer surface 6 toward the inner surface as shown in FIGS. 5 and 6. The main ball bearing 12 preferably has a diameter of approximately 0.5 inch, and the miniature ball bearings 17 preferably have diameters of about 0.06 inch. The main ball bearing 12 and the miniature ball bearings 17 are preferably manufactured from hardened steel, stainless steel or bronze.

FIG. 7 is a cut-away partial side view that illustrates a typical installation of the first embodiment 1 in a production oil well. In this example, a well casing 21 has been installed into a boring within a subsurface formation 22. A production tubing string that comprises a first piece of production tubing 23 and a second piece of production tubing 24 has been installed within the well casing 21, and one unit of the first embodiment 1 has been threadably inserted between the first piece of production tubing 23 and the second piece of production tubing 24. A string of sucker rod 25 has been inserted through the bore of the production tubing string and the bore of the first embodiment 1. The sucker rod 25 connects a downhole bailer pump (not shown) to a surface-mounted rocker pump (not shown). During pumping of the well, the sucker rod 25 moves generally up and down in relation to the production tubing string but can also move rotationally (laterally) from time to time in addition to the up-and-down motion.

Although a single unit of the first embodiment 1 is shown installed within the production tubing string in FIG. 7, multiple units of the present invention would typically be installed in the production tubing string along its length. FIG. 7 illustrates the first embodiment 1 deployed in a vertically oriented well. The present invention is also particularly useful to minimize friction between sucker rod and production tubing in wells that are sloped or curved because in these non-vertical wells, the sucker rod tends to contact and rub against one side of the production tubing string. The example shown in FIG. 7 represents the first embodiment 1 deployed with 1-inch API sucker rod having a maximum diameter of 1⅞-inch in an API 2⅞-inch external upset production tubing string that is set within API 5½-inch casing. The present invention is not limited to these particular dimensions, however.

FIG. 8 is a detail transverse cross-section view of the first embodiment 1 taken through the middle section 3 at the section line shown in FIG. 7, shown with a sucker rod 25 installed within the bore 11. As shown in this particular example, the sucker rod 25 is not centered within the bore  but is instead off-center and is in contact with two of the six main ball bearings 12, thereby reducing wear on the sucker rod 25 and on the inside surface of the production tubing string (not shown) that is installed above and below the first embodiment 1.

FIG. 9 is a side view of the second embodiment 26 of the present invention. The second embodiment 26 comprises a threaded upper section 2 and a threaded lower section 4 that are identical to those of the first embodiment 1, and a middle section 27 that is longer than that of the first embodiment 1. The second embodiment 26 has a total length of approximately 12.0 inches, with a middle section 27 having a length of approximately 6.5 inches. The middle section 27 comprises a first array 28 of friction-reducing units 9 with the centerline of the friction-reducing units 9 located about 0.75 inch below the top edge of the middle section 27, an array 29 of threaded holes 30 with the centerline of the threaded holes 30 located near the center (as measured from top to bottom) of the middle section 27, and a second array 31 of friction-reducing units 9 with the centerline of the friction-reducing units 9 located about 0.75 inch up from the bottom edge of the middle section 27.

The first array 28 and second array 31 each comprises six friction-reducing units 9 that are installed in a circular pattern around the middle section 27 in a configuration that is similar to the configuration described in reference to FIGS. 2 through 6 for the first embodiment 1. The angular orientation of the friction-reducing units 9 of the second array 31 is shifted by an angle α in relation to the angular orientation of the friction-reducing units 9 of the first array 28, as shown in FIGS. 10 and 12. The array 29 of threaded holes 30 comprises three holes 30, each having a diameter of about 0.37 inch and a depth of about 0.63 inch, with the three holes 30 positioned at equally-spaced angular intervals around the middle section 27, as shown more clearly in FIG. 11. The second embodiment 26 is manufactured from materials that are identical to those of the first embodiment 1.

FIG. 10 is a transverse cross-section, view of the first array 28 of friction-reducing units 9 of the second embodiment 26 (shown in FIG. 9), showing the angular positions of each friction-reduction unit 9, with the section line shown in FIG. 9.

FIG. 11 is a transverse cross-section view of the array 29 of threaded holes 30, showing the angular position of each of the three threaded holes 30, with the section line shown in FIG. 9. As shown, each threaded hole 30 extends from the outer surface 6 into the solid portion 7 but does not extend as far as the inner surface 8. The purpose of the threaded holes 30 is to receive stabilizer attachment screws that are described in reference to FIGS. 16-18. The protruding portions 13 of the six main ball bearings that extend into the bore 11 are also shown.

FIG. 12 is a transverse cross-section view of the second array 31 of friction-reducing units 9, showing the angular positions of each of the friction-reducing units 9, with the section line shown in FIG. 9. As shown in FIGS. 10 and 12, the friction-reducing units 9 of the second array 31 are rotated in relation to the friction-reducing units 9 of the first army 28 by angle α; i.e., each of the friction-reducing units of the second array 31 is not positioned directly below a corresponding friction-reducing unit 9 of the first array 28 but is instead offset by the angle α. For the second embodiment 26, the angle α is approximately 30 degrees.

FIG. 13 is a side view of the third embodiment 32 of the present invention. The third embodiment 32 comprises a threaded upper section 2 and a threaded lower section 4 that are identical to those of the first embodiment 1 (shown in FIG. 1) and the second embodiment 26 (shown in FIG. 9) and a middle section 33. The middle section 33 of the third embodiment 32 is identical in length to the middle section 27 of the second embodiment 26 (6.5 inches). The middle section 33 comprises a first array 34 of seven friction-reducing units 9 with the centerline of the friction-reducing units 9 located about 1.75 inches below the top edge of the middle section 33, an array 29 of threaded holes 30 with the centerline of the threaded holes 30 located near the center (as measured from top to bottom) of the middle section 33, and a second array 35 of seven friction-reducing units 9 located approximately 1.75 inches up from the bottom edge of the middle section 33. The array 29 of the third embodiment 32 is identical to the array 29 of the second embodiment 26 and described in reference to FIG. 11.

FIG. 14 is a transverse cross-section view of the first array 34 of friction-reducing units 9 of the third embodiment 32, showing the angular positions of each friction-reduction unit 9, with the section line shown in FIG. 13. As shown, the first array 34 comprises seven friction-reducing units 9 that are identical to the friction-reducing units 9 of the first embodiment 1 and the second embodiment 26. The seven friction-reducing units 9 are installed at equally-spaced angular intervals into ports 10 within the solid portion 7 of the middle section 33, in a circular array which lies in a plane that is perpendicular to the axis of the bore 11.

FIG. 15 is a transverse cross-section view of the second array 35 of friction-reducing units 9 of the third embodiment 32, showing the angular positions of each of the friction-reducing units 9, with the section line shown in FIG. 13. The seven friction-reducing units 9 are installed at equally-spaced angular intervals into ports 10 within the solid portion 7, in a circular array which lies in a plane that is perpendicular to the axis of the bore 11. As shown in FIGS. 14 and 15, the friction-reducing units 9 of the second array 35 are rotated in relation to the friction-reducing units 9 of the first array 34 by an angle b; each of the friction-reducing units of the second array 35 is not positioned directly below a corresponding friction-reducing units 9 of the first array 34 but is instead offset by the angle b, which is approximately 25.7 degrees in the third embodiment.

FIG. 16 is a side view of a stabilizer 36 that is designed to fit around and attach to a unit of the second embodiment 26 (shown in FIG. 9) or a unit of the third embodiment 32 (shown in FIG. 13). The purpose of the stabilizer 36 is to increase the effective outside diameter of the production tubing string, thereby reducing the magnitude of allowable pulsation movement of the production tubing string inside the well casing that may occur due to high velocity flows of liquids and gas within the production tubing string when the well is flowing. The stabilizer 36 is generally cylindrically shaped with tapered ends and comprises three cap screws 37 that are installed into a circular array of three screw holes 38 that are manufactured into the stabilizer 36, near the center (as measured from top to bottom) of the stabilizer 36, with one cap screw 37 and one screw hole 38 shown in FIG. 16. The three cap screws 37 threadably attach into the three threaded holes 30 of the second embodiment 26 or the third embodiment 32. The stabilizer 36 has an approximate length of 6.0 inches and an approximate maximum outside diameter of 5.0 inches. The stabilizer 36 is preferably manufactured from fiberglass-reinforced polymer.

FIG. 17 is an axial cross-section view of the stabilizer 36, with the section line taken through the center of one of the three screw holes 38, at the section line shown in FIG. 16. FIG. 17 shows a first cap screw 39 and a first screw fade 40 in cross section and also shows a portion of a second cap screw 41 protruding into the bore 42 of the stabilizer.

FIG. 18 is a transverse cross-section view of the stabilizer 36 taken through the centerline of the cap screws 37, shown with the cap screws 37 removed from the screw holes 38 for clarity. FIG. 18 shows the angular orientation of the cap screws 37 and the screw holes 38 within the stabilizer 36. As shown, the cap screws 37 and screw holes 38 are equally spaced at 120-degree intervals around the axis of the stabilizer.

FIG. 19 is a side view of a unit of the second embodiment 26 or the third embodiment 32 with a stabilizer 36 installed and held in place with the three cap screws 37 that are installed into the three screw holes 38, with one cap screw 37 and one screw hole 38 shown.

Although the first, second and third embodiments of the present invention are described as having a particular set of dimensions for the bore diameter, maximum outside diameter, and length, these dimensions may be varied so as to make any of the three embodiments compatible with a variety of sizes of sucker rod and production tubing. Similarly, the outside diameter of the stabilizer may be selected so as to make the present invention compatible with a variety of casing sizes.

Although the preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention. 

I claim:
 1. A friction-reducing device for use in a well bore, the friction-reducing device being cylindrically shaped with a tapered and partially threaded upper section, a cylindrical middle section, and a tapered and partially threaded lower section; wherein the middle section comprises a cylindrical outer surface, a cylindrical inner surface, a solid portion between the cylindrical outer surface and the cylindrical inner surface, and a first plurality of friction-reducing units; wherein the inner surface of the middle section forms a cylindrical bore in the center of the friction-reducing device, the cylindrical bore having a constant diameter from top to bottom; wherein the friction-reducing units are installed at equally-spaced angular intervals into ports within the solid portion of the middle section in a circular array that lies in a first plane that is perpendicular to a longitudinal axis of the cylindrical bore; wherein each friction-reducing unit comprises a rear bearing seat, an array of miniature ball bearings, and a main ball bearing with a protruding portion that extends through the inner surface of the middle section into the cylindrical bore of the friction-reducing device; wherein each port extends through the solid portion and penetrates both the outer surface and the inner surface of the middle section; wherein each port comprises a three-dimensional concave portion that penetrates the inner surface of the middle section; wherein the rear bearing seat of each friction-reducing unit comprises male threads around an outside circumference of the rear bearing seat that mate with female threads on an inside surface of the port; wherein the rear bearing sear further comprises a hex socket on an outside end of the rear bearing seat and a three-dimensional concave indentation on an inside end of the rear bearing seat; wherein the main ball bearing is positioned against the three-dimensional concave portion of the port, the three-dimensional concave portion of the port forming a front bearing seat for the main ball bearing; wherein the plurality of miniature ball bearings is situated between the three-dimensional concave indentation of the rear bearing seat and a portion of the main ball bearing that faces toward the outer surface of the middle section, and wherein the plurality of miniature ball bearings provides a low-friction rolling surface between the rear bearing seat and the main hall bearing; wherein the main ball bearing is free to rotate in any direction about any three-dimensional axis; and wherein the friction-reducing device is threadably inserted in-line between two adjacent lengths of production tubing, wherein a sucker rod is inserted through, the cylindrical bore of the friction-reducing device, and wherein the friction-reducing device maintains a gap between an inside wall of the production tubing and the sucker rod.
 2. The friction-reducing device of claim 1, wherein the upper section, the middle section, and the lower section are manufactured as a single unit from a single piece of machined steel.
 3. The friction-reducing device of claim 1, further comprising a second array of friction-reducing units identical to the first array of friction-reducing units except that the second array of friction-reducing units is installed in a circular array that lies in a second plane that is perpendicular to the longitudinal axis of the cylindrical bore, wherein the first and second arrays of friction-reducing units each has an angular orientation, and wherein the angular orientation of the second array of friction-reducing units is shifted by a certain angle in relation to the angular orientation of the first array of friction-reducing units.
 4. The friction-reducing device of claim 1, wherein the middle section further comprises a plurality of threaded holes that extend from the outer surface into the solid portion of the middle section but do not extend to the inner surface of the middle section, and wherein the threaded holes are configured to receive attachment screws for a stabilizer; the friction-reducing device further comprising a stabilizer that is secured to the middle section of the friction-reducing device via the attachment screws, wherein the production tubing has an outside diameter and a magnitude of pulsation movement within a well casing, the stabilizer being configured to increase the outside diameter of the production tubing, thereby reducing the magnitude of pulsation movement of the production tubing inside the well casing. 